The present invention relates to valves, and more particularly to a butterfly valve having a disk with a shaped edge in predetermined locations on the disk to create flow openings between the disk and a valve wall for defining a flow characteristic of the valve.
Conventional butterfly valves operate by positioning a disk within a valve body to control fluid flow through the valve body. The disk rotates about a pivot point or axis defined by a shaft mounted within the valve body. Rotation of the disk, resulting from a torque applied to the shaft, creates or reduces an opening for fluid to flow through the valve body. As the disk is rotated from a closed position (typically vertical) to a fully open position (typically almost horizontal), the flow area through which the fluid can flow increases. The fluid flow can be somewhat controlled by adjusting the angle of rotation of the disk within the valve body. Numerous advances have been made in conventional butterfly valve design to reduce the torque required to operate the valve and to extend the rotational range during operation.
Compared with other types of control valves, for example globe valves, butterfly valves provide a relatively high flow capacity for relatively lower cost. Thus, for specific applications, butterfly valves are very economical. In the alternative, conventional butterfly valves have limited application in process control due to the inherent flow characteristics of these valves. As understood by one of ordinary skill in the art, the butterfly valves are better suited for On-Off flow control applications. Numerous process control applications require precise flow control through the entire operational range of the control valve. When precise flow control is required, rotary ball valves are normally installed, rather than butterfly valves.
Additionally, certain processes require specific or precise inherent or installed flow characteristics. As understood by those skilled in the art, the flow characteristic of a control valve is the ratio between the flow coefficient (Cv) and the travel in degrees of rotation of the disk. This design parameter defines the rate flow through a valve based upon the percent of rate of travel, or the physical position of the control element within the valve body. For example, applications in liquid level control with constant pressure benefit from a linear flow characteristic within the valve.
An additional factor in the application of butterfly valves relates to improving the dynamic torque characteristic of the control valve. As the fluid flows through the valve, a force is applied to the disk by the fluid. In general, as the flow rate increases through the valve, greater force is exerted upon the disk. These increased dynamic forces require more torque to rotate the disk. The amount of torque required to rotate the disk during operation varies depending on type of fluid flowing through the valve, the shape of the disk and the position or orientation of the disk. It is advantageous to lower the torque in a given application. Lower torque requires a smaller actuator to operate the valve, thereby saving physical size and further reducing cost.
Additionally, conventional butterfly valves that operate through 90 degrees of rotation, can experience a torque reversal when the disk rotation approaches 70-80 degrees. At this point of disk rotation, the force exerted upon the disk by the dynamic torque changes from one side of the disk to the opposite side of the disk. Eliminating this reversal potential from the operating characteristics of the butterfly valve results in more stable valve positioning and significantly reduces the possibility for damage to the actuator or valve.
There is a need in the art for a butterfly valve having improved flow characteristics and improved dynamic torque characteristics. The present invention is directed to further solutions that address this need.
In accordance with one example embodiment of the present invention, a disk for controlling fluid flow inside a valve is provided. The disk includes a sealing surface for sealing with a valve seal when the disk is in a closed position. The sealing surface includes a shaped edge that creates a flow opening with the valve seal as the disk pivots from a closed position toward an open position, such that a profile and location of the shaped edge defines a size of the flow opening at predetermined disk positions to characterize fluid flow therethrough. The shaped edge is an instrument that provides greater opportunity for modifying the flow characteristics. By altering the shape and location of the shaped edge on the disk, the flow characteristics can be modified to create a desired flow characteristic result. The shaped edge further provides for more flow rate control when the disk is partially opened, and also enables a smoother transition between open and closed valve positions.
In accordance with further aspects of the present invention, the disk is disposed offset from a center axis through a pivot point of the disk. An indentation can be provided, formed along the upstream side of the disk for dynamic torque reduction. The indentation includes at least one of a substantially concave curved surface and a ramp surface angled relative to a vertical axis. The disk is suitable for use in a butterfly valve.
In accordance with still further aspects of the present invention, a substantial portion of a planar surface of the disk is angularly offset from a remaining planar surface of the disk to hinder dynamic torque reversal. A cross-sectional thickness of the disk can be relatively smaller at a trailing edge of the disk than a cross-sectional thickness of the disk at a leading edge of the disk.
In accordance with another aspect of the present invention, the shaped-edge is in the form of a curved profile. Alternatively, the shaped edge can include a profile that angles away from the valve seal as the disk rotates about the pivot point to transition from the closed position to the open position. The shaped edge can also be disposed along at least a portion of a downstream side of the disk. The shaped edge can further be disposed proximal to a leading edge of the disk.
In accordance with one embodiment of the present invention, a valve is provided. The valve includes a pivotable disk. The disk includes a sealing surface for sealing with a valve seal when the disk is in a closed position. The sealing surface includes a shaped edge that creates a flow opening with the valve seal as the disk pivots from a closed position toward an open position, such that profile and location of the shaped edge defines a size of the flow opening at predetermined disk positions to characterize fluid flow therethrough.
In accordance with still another aspect of the present invention, a wall of a valve housing is substantially concave to enable the disk to rotate in close proximity to the wall to further characterize fluid flow.